I have read in some spots that the louvre filter basically is like vinetian blinds for the tv, blocking light from above. If the TV is going to be mounted above a fireplace, fairly high up, with only a light about 12 feet away in the next room over, will the filter even have any effect? Will just having a dimly lit room affect the blacks noticeably on the UT50 or does the light have to be fairly significant?

I've found on the ST50 that the filter seems to be for blocking light from above like a ceiling light.
This causes reduced contrast if you view the TV at an angle above the display.
My ST50 is on a table stand that is at eye-level when I am sitting on the couch, but if I stand up the image is lower contrast and washed out.
I can however sit on the floor at a level below the display and thats OK like viewing at eye-level.

I wish they made a model without the filter like the UT50, but with the other features of the ST50 or GT50 like extra HDMI ports, custom mode with pro settings, etc.

You mean you wish the ST50 had the option of a variant model without the filter. Basically saying the same thing, lol. That's what panasonic should of done like a 1.0 and 1.1 ver. of same model... or better yet if they wanted to maintain their profit ratio give that as a less costly option. Then they wouldn't need a UT50 model AT ALL and boost their ST50 profit line elasticity sales 3-4 fold. I suspect it would be an est. $100 less at wholesale cost level. The difference at wholesale cost level between a UT50 and ST50 is roughly $200. Adding an extra hdmi and update the software cost basically nothing. Ok, maybe $5 at manufacturing cost level if that. So at wholesale level the cost would drop an est $100 bucks for losing the louvre filter and add $10 at wholesale for s/w and extra hdmi. You're talking roughly $150 retail less than current priced ST50 model. That's nothing. Current retail price difference between an ST and UT 50 is approx $260. Dropping that by $150 means to upgrade to an ST50 1.1 version would just be $110 increase retail. The current UT50 customers have no problem paying that extra to upgrade to a ST50 line and boost Panasonic profits overall. I think it's a dumb move to make a UT50 line financially. In fact retail wise, the price of the UT50 have dropped waay more than ST50 which have spiked up in sales due to excellent reviews across the board and maintained their profit ratio.